> > One thing to be careful is if you are relying on 'transactions' to handle anything. Obviously the transaction has to be in the same connection just to work. Despite what others have said, the PDO connection will be different to the generic mysql connection as it is a separate process. Persistent connections will only reuse an already open connection, you can't connect two processes to the same connection. You would not know which process was accessing things. According to the documentation: "First, when connecting, the function would first try to find a (persistent) link that's already open with the same host, username and password. If one is found, an identifier for it will be returned instead of opening a new connection." Therefore, providing you've configured PHP's --with-mysql and --with-pdo-mysql options with the same MySQL library, then as long as the host, username and password are the same, the same connection will be re-used for both the native (mysql_pconnect) connection and the PDO connection. I'm not sure about the mysqli library, but I believe that lies beneath the mysql_* family of functions anyway so it shouldn't make a difference whether you're using libmysqlclient or mysqli. Regards, Andy